a) Field of the Invention
This invention relates to the treatment, disposal or management of waste, in particular waste plastics.
Plastics in one form or another enters into almost every aspect of our daily lives. Expanded polystyrene (EPS) which is well known and used for its insulation and shock absorbent properties because it has the characteristics of 3 to 7% solids and 95 to 99% air or blowing agent is encountered in fast food restaurants as clam shell containers for hamburgers and drinks cups, as plates and trays in sandwich bars and fish and chip shops, as pizza trays, as agricultural containers for seeds and plants; as alternative disposable cups and plates etc., to conventional crockery, as cups at vending machines as yoghurt and frozen yoghurt pots, as boxes to transport certain perishable foods such as fish and eggs, as fruit trays, and as protective packaging for a wide range of goods such as telephones, so-called white goods, e.g. refrigerators and cookers, and televisions.
The consumption of plastics cups alone, mainly from vending machines, has reached some 3,000,000 per day in the UK and 60,000,000 per day in the U.S.A. where, in one factory with around 500 staff, it was ascertained that as many as 3000 cups were consumed in one day.
Other plastics materials which are in common use are as follows: polyethylene which as high density and low density polyethylene (PE) is used for containers such as refuse sacks, carrier bags and even specialist containers such as blood and plastic containers and as expanded polyethylene (EPE) is used in film or in sheet form for protective wrapping and packaging easily damaged items in the electronics, glass, china and furnishing industries; polystyrene (PS), high impact polystyrene (HIPS) which is used for making cutlery and some kinds of beverage cups; Oriented polystyrene (OPS) as used in the packaging catering and confectionary industry polyvinylychloride (PVC) which is somewhat clear and is used for packaging and wrapping films and for containers such as blister type packages for articles of various kinds; ABS which is used for many kinds of containers such as cups, yoghurt pots and butter and margarine containers; polypropylene (PP) which can be very clear and is used in general packaging where a clear view of the packaged article is required without discoloration, eg for food containers as the container covers and for packaging clothing such as shirts, and other articles such as sheets and curtains, and expanded polypropylene (EPP) which is used for its insulation and impact resistance properties as say end blocks for transporting computers and for automobile bumpers or fenders.
In fast food restaurants the consumption of plastics is monumental, and represents a considerable problem. Staff have to be diverted away from profitable work to empty the waste containers which can cost up to 45 per hour. Moreover, it has become the vogue in U.S.A. for a dinner party, picnic or barbecue, to avoid any washing up to have total replacement plastics so that all that needs to be done after the meal is to wrap up everything in a plastics table cloth and throw away to the garbage bin.
Whilst plastics and articles made therefrom are relatively inexpensive to manufacture, are inert and do not contribute towards the continuing destruction of our natural timber resources as does the production of paper, plastics are increasingly being given a bad press because of the problems plastics waste causes to the environment. The advantages of the inertness of plastics become disadvantageous when it comes to their disposal as the plastics does not dissolve in the ground or otherwise biodegrade. Incineration is not the answer because of the emission of "greenhouse" gases and the danger of emission of noxious gases, if carbonization occurs which can require the cost prohibitive installation of suitable filtration equipment.
The search for a satisfactory biodegradable plastics has still not been really successful. Currently available biodegradable plastics reduce shelf life which encourage waste and consumption and generally are starch based around a plastics "skeleton" anyway. In any event, there has been no reliable body of evidence that biodegradable plastics will not harm the environment. An all too familiar sight nowadays is the presence of waste plastics in the environment, presenting a hazard to wild life and being a continual eyesore. It is blown around our towns and cities, into the parks, about the countryside; it is present at the seaside and on the beaches, it floats in the seas and oceans and can end up in places which have not hitherto been visited by human beings. Imagine that 200,000 tons of waste EPC would cover the surface of the world to a depth of one foot.
The principal method of disposing of plastics waste is by burying in landfill sites. In the UK alone, it is estimated that 1.4 million tonnes of waste plastics is buried each year in landfill sites around the country. Approximately 5% by weight and 50% by volume is attributed to EPS. In an untreated state, backfilling "raw EPS" consumes a site's capacity inefficiently and deems the landfill site useless for all but the most basic of uses. Obviously, building on such landfill sites cannot be entertained because of the danger of subsidence. Moreover, landfill sites are becoming increasingly remote from the points of refuse collection, thereby further increasing transportation costs.
Moreover, because of its high volume to low weight ratio (particularly EPS products) the cost of transporting plastics waste to landfill sites, is enormous. The human resource and the amount of fossil fuels consumed in transportation are high and the latter also contributes in no small way to environmental pollution. Moreover, sites available for landfill are becoming increasingly scarce. In countries such as Germany where the geological structure prohibits landfill (the underlying rock is very near the surface) the waste plastics to be disposed of by landfill has to be transported to another country, e.g. France, where landfill is possible and sites are available. In Japan 85% of the people live on 10% of the land, so incineration wins over landfill as the waste plastics treatment of choice.
And, if nothing is done, the situation can only get worse because the population of the world has grown from around 2.5 billion in 1948 to 5 billion at this time--in 1991--and is now increasing by about 83 million each year. It has been stated that to satisfy the needs and expectations of this population explosion, the Earth's natural resources and species are being destroyed and polluted on a scale which is now threatening the very life support systems of our planet. The havoc being inflicted on our habitat ranges from damage to the ozone layer, to destruction of the tropical rain forests; from pollution of land and water to desertification and the wholesale extinction of animal and plant species.
Due to environmental pressure, there is a backlash against the use of plastics which is beginning to cause its replacement by paper and cardboard in certain areas, eg. egg boxes, plates, cups, and clam shell containers. One industry in which replacement has begun in the USA is in the fast food industry. However, this is environmentally unsound as the more paper and cardboard that is used, the greater is the depletion of our natural timber resources. And contrary to popular belief, paper and cardboard does not readily biodegrade, particularly in dry conditions which can be encountered in some landfill sites and the affect of printing inks on the environment has still not been fully assessed. Indeed, the leachate released from paper and cardboard degradation in landfill sites could pollute water supplies and create methane gas with its attendant problems. All around there is a growing environmental pressure, not only to find replacement materials for plastics which will not pollute the environment and to step up research into biodegradradable plastics, but also to dispose of the enormous volume of plastics waste in a more efficient and environmentally friendly manner. All plastics waste must be contained on board ships, at sea, due to recently passed International Maritime Laws, which is a major problem as a high percentage of the waste is contaminated with organic matter.
The focus of mainstream research, nowadays, is on recycling. Recycling for reuse has become the name on everyone's lips and a function which most of us perform to some degree or another. Recycled paper is in common use. eg for envelopes, but it is not generally known that the chemicals used to dissolve the printers ink out of say newsprint and printed paper and cardboard packaging produces an effluent which is extremely damaging to the environment. Moreover, the energy consumed in the recycling of paper and cardboard is not low.
Recycling has become of such importance that bottle banks have become a common sight in our towns and cities, and door to door collection of waste paper and textiles have become a feature of our lives. Skips are available also for the disposal of waste which is not mixed up with organic materials of the kind ordinarily found in domestic and industrial refuse. Thus, such skips which contain glass, cardboard, paper, wood, textiles, metals and plastics films and plastic bottles from domestic and industrial sources can be collected and taken to a recycling plant. One such recycling plant sorts the glass, metals, wood, contaminates, plastics, paper textiles, waste and burnables from each other. The plastics and paper are fed to a bale press, the bales are fed to a shredder, and the shredded plastics washed, dewatered, dried and then sorted with hydrocyclones. The sorted plastics is fed to an extruder and the molten plastics passed through a die which produces plastics threads that are cut into pellets by means of rotating blades. The plastics pellets are packaged to be ultimately formed into lower grade plastics products such as coat hangers, flower pots, garden hoses, pipes, sheeting and bottles etc. The plastics is downgraded, because of its melt history, being a mixture of different kinds of plastics and cannot take colour pigments, so that the products end up a dull grey/brown/green colour.
Another plastics recycling process uses waste articles made mainly from thermoplastics, in particular high and low density polyethylene and polypropylene. Other thermoplastics such as PET and ABS can be recycled but under certain controls and PVC may only be present in small proportions without special additives being used. The sources of new material for this process are manufacturers of plastics articles, ie, film, bags, tableware, syringes, toys, book bindings, trays, various domestic articles, e.g. containers and bottles, milk, suppliers who produce their own plastic milk bottles and who have redundant and broken milk crates, beverage companies who use plastics bottles and containers, and who have broken beer crates, large volumes of below standard articles, e.g. piping, ducting, plastics joints, disposable plastics medical goods, head waste from manufacturers of plastics articles from starting up the machine and after shutdown, plastics packaging to be disposed of by manufacturers, distributers and retailers and contaminated or sub-standard granules from plastics processors.
The collected plastics material is sorted, granulated, mixed/blended and then plasticized in an extruder consisting of a large steel screw in a heated steel barrel, by means of the friction caused by the rotating screw melting the plastics. The plastics used in this process can include up to 1% contaminants, such as paper, but any more can cause unacceptable wear to the extruder barrel and screw. Because of this wear, the use of contaminated plastics in extruders which are in general use in recycling to reuse is prohibitive above 1% contamination level. Extruders are expensive machinery whose parts are expensive to replace, require skilled and specialist operators and can generally only be used to recycle homogenous plastics waste. This process can produce basic solid plastics elongated product such as posts, poles, stakes, boards and a variety of similar shaped products, but again the plastics is of down graded nature and could not be mixed with virgin plastics. Specific use of the product are slatted floors for farm animals, pallets, underground cable covers, fencing posts and street and road furniture. Again these products are a dull colour as they cannot accept colour pigments but special painting and one-colour plastic coating processes have been devised.
Another recycling process involves the plastics cups supplied by the makers of beverage vending machines. One supplier has devised a method of collection from the sites of use. This involves supplying collection receptacles with drip trays at the vending machine locations and arranging for periodical collections. One collection cycle involves two trucks, two drivers and three support staff. It has been found that the collection receptacles for these plastic cups can contain as little as 40% by weight plastics waste and as much as 60% by weight organic waste comprising say, coffee, milk, sugar, soup etc. This can result in a hygiene problem as the organic material in the collection receptacles begins to support bacterial growth and to smell, giving rise to complaints. The plastics cups have to be cleaned to remove the organic contaminants before being recycled to reuse using known extrusion techniques. And even though one would have thought that the same plastics used for all the cups would be identical, variations do occur in the same plastics from different manufacturers, eg Mobil and Shell, which results in downgraded recycled plastics product.
It is worth at this stage examining more closely the thoughts behind re-cycling. As well as endeavouring to protect the environment, one of the main factors in re-cycling is to preserve the natural resources of oil and gas. It is a recorded fact that of the volume of oil produced only 5% is used in the packaging industry, 95% is burnt, the majority by the internal combustion engine. It would be a brave government that would tackle that particular problem head on. So ever eager to win votes without taking risks they have targeted the packaging industry as being the main aim in their legislation for re-cycling. However, it is important to recognise that environmental protection must encompass the use of all resources, including labour, land, materials and capital energy.
If therefore the stated aim is to protect natural resources does the question of re-using waste EPS stand up to scrutiny ? As already mentioned, the treatment of downstream post consumer plastics (that is plastics waste) presents inherent difficulties.
1. There needs to be separation of the waste into polymer type according to compatibility,
2. It needs to be washed, with the consequent use of a resource which we are told will become scarcer due to global warming,
3. It needs sophisticated separation machinery, which is energy consuming,
4. The capital cost is high, an effective plant could be in excess of 1,000,000.00.
5. The problem of transporting the waste to the plant is still relative to the 90% or so of air or blowing agent that is being carried.
6. The excess movement of heavy vehicles is damaging to the infrastructure and the exhaust emissions are environmentally unfriendly.
The total use of energy is calculated to be nearly three times as much as that used to produce the original packaging. How then is it possible to conserve the source of energy and yet satisfy the demands of the governmental bodies for extending the life of the plastics?
Any person of ordinary skill in the art in the plastics industry would tell you nowadays that the way to handle EPS waste is to burn it. Incineration plants have been set up, which have been successful in burning mixed waste, but there are shoals of statistics which will tell you how profligate we are to waste this energy source and there is the high capital cost of the plant.
Whatever, may be said in public the Applicants' research shows that there is no firm operating recycling without incurring a significant loss in the process. Some recent French research concluded that only 70% of costs are recovered in a typical recycling operation. Also, in logic, recycling does not solve environmental problems. It operates merely to delay the disposal of plastics by the community. Thus recycling processes, in making a loss, are in the final analysis environmentally unacceptable as they deplete both capital and human resources.
Accordingly, plastics produced for reuse from plastics waste which has been recycled cannot compete with regard to cost and quality with virgin plastics, unless one is dealing with uncontaminated factory scrap plastics which can be fed back into the processing chain for extrusion. Contaminated plastics waste has to be subjected to a number of operations before it is suitable for granulation or pelletization, such as crushing, shredding, sorting, washing, dewatering and drying. Moreover, there is some plastics waste such as computer, audio and video tapes and floppy discs which because they incorporate metal oxide, and are contained by cassettes of different plastics materials cannot be recycled in currently available recycling plant. And moreover, incineration is prohibited because metal oxides when burnt give off noxious gases.
Credit cards which have to be destroyed for one reason or another, eg because of mistakes made in personal details during manufacture present problems as they are contaminated with metals and print. At present damaged credit cards are presented edge on to a shredder and are collected for transport to an incinerator. But it has been known for cards to miss the shredder knives and thereby give rise to a security risk. Moreover, expired credit cards are normally destroyed by cutting in pieces and disposed of into the refuse cycle. This represents a considerable quantity as, in the U.S. alone around one billion credit cards are in circulation at the present time.
Even EPS used in a protective role in packaging is more often than not contaminated with eg wood slivers from pallets, bar codes made of paper or cardboard, and shrink wrap or straps made of different plastics material.
EPS fish boxes, which because of their insulation properties, can give at least an extra day's "shelf" life to the packed fish once removed from refrigeration, present particular problems in disposal. This is because, once used, they are contaminated with fish scales and slime, become smelly and are a health hazard. Moreover, used fish boxes have a high degree of salinity thereby precluding reduction in size by shredders and presses which would "rust" up. So, hitherto, used fish boxes have been burnt (incinerated) or disposed of by landfill. Neither of these courses is immediately open in one instance known to the Applicants, where a hotel in Europe which is snow bound during the winter, has to store large quantities of EPS fish in fish boxes to last the winter. All that can be done until the spring thaw when the roads are open to transport is to spray the used fish boxes with disinfectants to reduce the stench and minimize health hazard.
Even the waste EPS from fish box manufacturing factories cannot readily be reused because once the waste has hit the floor, so to speak, it cannot be used for food. Thus, the waste EPS has to be continuously removed. Applicants have ascertained that in one UK fish box factory, the amount of waste EPS is so high that four skips full per day have to be transported to landfill. But EPS saves the fish industry around $10,000,000 a day because it increases the shelf life subsequent to removal from refrigerated stores.
Used disposable plastics nappies or diapers which, in addition to the outer liner make use of special absorbent plastics also present a disposal problem as they cannot be flushed away into the sewage system and may also be heavily contaminated with waste organic matter which leaves incineration and landfill again as the only options available.
Plastics medical waste also presents a problem all of its own; particularly where disposable plastics syringes are concerned in view of the danger of the transfer of fatal diseases such as AIDS and Hepatitis B from accidental needle strike. Not only is plastics medical waste contaminated with organic material but also in some instances with metal of which the prime example is syringes.
In addition to the drive to recycle waste plastics to reuse to make new products, environmentalists are also pressing for a reduction in the amount of plastics packaging used overall and reuse of plastics packaging as many times as possible.
Examination of these options with regard to EPS results in the finding that each has its drawbacks.
Modern packaging has been developed to cope with the demands of modern living, and it is because of this development that it is now possible to reduce considerably the amount of damages experience in the transit of goods. It is also true to say that the insulation and sealing of food has helped to increase the shelf life of many food products. It is therefore difficult to see an economic alternative.
Indeed, a leading German research firm has assessed what would be the environmental impact if plastics packaging was replaced by the best alternative in each individual application. The results were most significant and one: Energy consumption would double; raw material consumption would quadruple; the volume of waste would increase by 150%; and the cost of packaging would double.
To reuse the goods is laudable but in certain industries such as food this would not be practical because of the contamination of the wrappings.
The plastics industry is seen to be very efficient at reclaiming it's own waste at source. The fact that there is a percentage of the blowing agent left and the fact that the materials are homogeneous makes it easy to re-introduce the waste into the manufacturing process. It is claimed that the waste factor is now as little as 1%. However, when the plastics packaging is moved downstream to the end consumer, problems begin to arise. Firstly, as has already been discussed, to be, properly processed the plastics need a complimentary polymer profile. Secondly it is inevitable that the product will become contaminated in use.
Thus, landfill is still the most popular way of management of plastics waste, despite all its disadvantages. But there has increasingly become a desperate need for environmental reasons to solve the problem of plastics waste management as landfill sites are becoming more and more scarce, the pressure from environmental groups is increasing and recycling as the sole alternative is financially unviable.
b) Description of the Prior Art
Applicants are aware of known apparatus for melting plastics waste, all of which cannot cope with contaminated plastics waste for reasons which will readily become apparent.
Thus, DE Gebrauchmuster G 85 25 903.9 discloses an apparatus for the destruction of data stored on microfilm to guard against reenlarging and espionage, by liquifying the film material in an electrically heated sealed metal container which has electrical heating elements in its wall. The metal container has a specially designed nozzle situated in its base through which the liquid material is removed in droplet form i.e. an interrupted flow, under gravity. The droplets are converted into granules by the cooling action of air on the granules as they fall over a set distance into a receiving container which can be pulled out like a drawer. Interrupted droplet flow is essential to such apparatus in order to produce a granule size which would prevent the possibility of any reading by reenlargement. Such an apparatus would not work with contaminated plastics waste as the contaminants would block the fine nozzle and the disposition of the heating elements would not provide the requisite melting effect.
Patent Abstracts of Japan, volume 9 No. 311 (M-436) (2034), Dec. 7, 1985 and JP A, 60145809 (Masaki Tomizawa) Aug. 1, 1985 disclose a method of lowering the treatment cost of waste resin by providing a combustion resin passage for feeding part of waste resin that has been melted in a melting tank by steam pipes and by a heating burner to a resin burner where it is burnt. When the resin burner becomes operated in a steady manner, the heating burner is stopped and the apparatus is operated using only heat from the resin burner. Waste resin from the melting tank runs downwards under gravity through a resin discharge pipe and is heated by molten resin running through a passage which feeds the resin burner and surrounds the middle and upper portions of the discharge pipe. Again, such an apparatus would not function with contaminated plastics waste because the passage ways and discharge pipes would become blocked. and resin burning is environmentally unfriendly in giving rise to greenhouse gases.
In GB 1,572,623 a combination of a melt chamber and an extrusion screw is used to produce molten plastics from foamed thermoplastics head waste of scraps, odds and ends, chips and cut ends produced during the processing of plastics and synthetic resins for producing good quality recycled pellets. The extrusion screw extends horizontally beneath and is fed from an elongate melting chamber which is V-shaped in cross-section and extrudes threads of plastics through a suitable die. To prevent reverse upward movement of the foamed plastics waste, the melting chamber is provided with a plurality of fins which project towards each other from the chamber walls on opposite sides of the V. As has already been explained, such apparatus, in using an extruder is expensive, to buy, operate and maintain, and cannot deal with plastics waste which has greater than 1% of contaminant and even this percentage will depend upon the nature of the contaminant. Some contaminants will cause blockage of the extruder and others will cause unacceptable wear to the extruder screw and barrel involving enormous replacement expenditure.
In another apparatus involving an extruder, the extrusion screw is arranged vertically but this apparatus suffers from the same disadvantages as those of an extruder having a horizontal screw.
With apparatus involving extrusion, additional pressure is required to melt the plastics waste and to force the molten plastics waste through a die.
It is within this context and in response to a long felt want that the Applicants' invention was born.